This invention relates to a waterproofing material suitable for waterproofing ponds, lakes, lagoons or comparable sites whereby water is retained, or wherein waste is deposited and the ground beneath has to be protected against leakage of aqueous or other liquid. The material can also be used in relation to water proofing structures, covering contaminated land to prevent flow of water into such contaminated land and lining trenches which separate contaminated areas from clear areas. The material can also be used as roofing material on flat or sloping roofs.
Several materials have been proposed in the past which include a layer of swellable smectite such as montmorillonite and/or saponite incorporated within the material to act as the sealing agent. The montmorillonite has been carried by a support layer or base which has been provided in various ways. A support layer acts as protection but also gives additional strength within the material.
European patent number 59625 (CLEM) describes a waterproofing material which is a laminate comprising a fabric base, particles of montmorillonite adhered to the base and a scrim adhered over the montmorillonite particles to retain them on the base.
In European patent application 246 311 (McGROARTY) a lower sheet comprises a base and montmorillonite and an overlaid sheet comprises a base and montmorillonite. The bases are of solid plastics non-venting and impermeable material so one of the bases forms a non-water transmissive layer between the two layers of montmorillonite, thus giving a very good seal. However, the McGROARTY construction does have several practical difficulties. Firstly, the bases are made from a thick, impervious and essentially solid plastics material, described in the specification as HDPE (high density polyethylene). Secondly, the granules of montmorillonite are adhered not only to the base but also to each other.
Waterproofing materials of this kind are usually supplied in rolls and have to be unrolled and placed to lie in the pond, lagoon or storage space. With the bases made from HDPE the McGROARTY material is less flexible than when using a fabric (non-woven or woven) for the base. This means that the product is much more difficult to handle and the montmorillonite is likely to crack during folding and unfolding. Further, because of the nature of an HDPE plastic sheet the adhering of the montmorillonite to its surface is not easy. Quite large quantities of very strong glue have to be used.
A further waterproofing barrier material is disclosed in GB 2 202 185 (NAUE) in which a layer of montmorillonite is sandwiched between a pair of layers of non-woven textile material and the two layers are united by needling, the needles passing through the layer of montmorillonite and uniting all three layers. Again, because the montmorillonite is not adhered to the layers, as the material is unfolded, folded and manhandled during installation, the montmorillonite can move relative to the two layers leaving voids and/or more permeable thinner areas in the montmorillonite layer.
There is a further disadvantage in that all these earlier materials tend to use particulate montmorillonite which may be from 2-5 mm, usually about 3 mm in size. Although finer material can be poured to fill gaps between the larger granules, such larger size granules tend to make up the bulk of the montmorillonite layer in the waterproofing material. As the waterproofing material is only relatively thin, for example containing only perhaps one or two layers of montmorillonite granules, problems can arise in connection with foreign bodies in the montmorillonite used. In its natural state montmorillonite is found alongside shale and other impurities. Whilst the montmorillonite can be quite highly purified, it is not unusual for a low percentage of shale particles to remain in the final sized and graded montmorillonite. An unfortunate result of the use of relatively large granules of montmorillonite is that granules of impurities can also become incorporated in the material. The chemical nature of shale and some other impurities have the effect that not only are they not montmorillonite (and therefore do not swell upon contact with water), but, when wetted, act to inhibit swelling in adjacent montmorillonite granules. Thus, a single granule of shale in a layer of waterproofing material can form a small area (perhaps 10 mm in diameter) which does not swell upon being contacted with water. Such areas are generally water impermeable, but medium and larger such areas allow water to pass through the sheet. When water pressure is high this flow can cause significant wash out of adjacent montmorillonite leading to failure of the sealing system. Although the percentage of impurities is small, and although the failure rate is small, when a large area is sealed using sheet material incorporating such impurities it needs only a single leak for the whole system to have failed. A pond or lagoon which has a single leak is no pond or lagoon at all!
U.S. Pat. No. 2,277,286 (Bechtner) is primarily concerned with formation of a blanket of dry xe2x80x9cin-situxe2x80x9d bentonite which has all the disadvantages noted above, and is also difficult to distribute evenly. However, it also mentions the possible formation of a putty-like mass form 50-60% water and 40-50% clay, which is sufficiently cohesive to adhere to rough or smooth surfaces, such as a wall which is to be sealed against leakage from outside earth.
Particulate montmorillonite has also been mixed with various organic components to form a thick putty (see U.S. Pat. No. 4,534,925). Typical components are polypropene and polybutene. This material has been extruded in the form of rods and sheets, usually being stored between layers of release paper. Such material has been used for sealing ground foundations and similar structures. It has not, however, being extruded so as to become united with a carrier sheet and be capable of use in large rolls for covering large areas. Indeed, the polypropene and polybutene used is intended deliberately to give the extruded material a rubbery or formable consistency enabling it to be moulded by hand around small areas such as chimneys, at joints in concrete panels, or where drains penetrate foundations. These materials are also quite expensive and prohibitively so for use in relation to large area sheets.
U.S. Pat. No. 5,116,413 (Nooren) teaches the mixing of bentonite clay with a hydrophobic substance such as bitumen or vaseline, with addition of only a small amount of water or alcohol, namely 0-4% (see column 4 line 44), to provide a sealing agent which is mouldable and useful for production of watertight bushings. Cellulose compounds or polyacrylates are mentioned as alternative water swellable or swollen high-molecular substances to the bentonite clay.
U.S. Pat. No. 5,132,021 (Alexander) is primarily concerned with use of dry, particulate bentonite clay sandwiched between outer sheets. At column 7, line 26 to 33 it mentions that polar activators such as 75-98% methanol or ethanol and 25-2% water can be xe2x80x9cincluded with (absorbed by)xe2x80x9d the clays, the amount of such activator being from 10-40% relative to the dry weight of the clay. Partial hydration of the clay should result from the aforesaid addition. However, there is no teaching at all of the mixing of the two constituents, or kneading same, to provide a substantially homogeneous deformable mass. Without this, a reliable waterproofing layer is not formed. The mere pouring of water onto the xe2x80x9cin situxe2x80x9d dry clay will be quite inadequate in most applications, as discussed above.
U.S. Pat. No. 5,237,945 (White et al) teaches the application of a bentonite clay/water paste (preferably about 30% clay) to the top surface of a loose fibrous mat in which powdered clay has been deposited. The paste is subsequently compressed into the mat, which in practice is likely to prove difficult, and certainly will not provide a truly homogenous hydrated layer, nor retain or hydrate the loose particles.
Calcium montmorillonite is sometimes used as a substitute for sodium montmorillonite. In use, calcium bentonite, when initially wetted, will swell and expand in the same way as sodium montmorillonite. However, if the material should dry out, for example due to low rain fall or a falling water table calcium montmorillonite cannot shrink back to its original size upon loss of water without cracking. After cracking and upon re-wetting the clay can not re-wet so as to reform the waterproof barrier. Thus, a calcium bentonite waterproofing material should only be used in cases where permanent wetness is to be encountered.
All sodium containing montmorillonites do have a problem when the water which comes into contact with them is contaminated by salts, particularly sea water or other salts which render the ground water ionised and highly active. In ground water calcium is invariably present in quantity from soil and minerals. When such ionic calcium comes into contact with montmorillonite it tends to convert the montmorillonite from the sodium to the calcium form with the disadvantage which has been outlined above.
This particular process makes it generally unwise to use even sodium montmorillonite in a situation where the ground water can become rapidly ionised or contaminated by leachates or the like. In particular, fertilisers are a particularly notorious cause of ground water ionisation and can cause sodium montmorillonite break down.
In a paper entitled xe2x80x9cPreparation of Montmorillonitexe2x80x94Polyacrylate Intercalation Compounds and the Water Absorbing Propertyxe2x80x9d by Ogawa et al published in Clay Science Number 7 243 251 (1989), the authors have described the introduction of a acrylamide into montmorillonite and the polymerisation of the acrylamide to form a polyacrylamide intercalation compound. The enhanced water-absorbing properties of the compound are noted.
It is to be appreciated, of course, that the processes carried out in the Ogawa paper were essentially laboratory processes involving small amounts of material. No techniques were described for making any useful product and there was no discussion of the advantages of high density such compounds as waterproofing agents.
It is an object of the present invention to provide a waterproofing material in sheet form whereby the above described disadvantages of mats incorporating dry or semi-hydrated particles (hydrated in situ), are reduced or minimised.
It is a further object to provide a waterproofing sheet which is reliably waterproof, and not subject to leakage in small local areas.
It is yet another object of the invention to provide a waterproofing material in sheet form which is less susceptible then hitherto to damage by leachates or salt water.
It is yet another object of the invention to provide a denser, and consequently less bulky and easier to handle waterproofing material in sheet form than hitherto.
The invention provides a novel method of making a waterproofing laminate material comprising the steps of mixing a particulate smectite clay with a liquid to form a mixture, said mixture containing clay in a range from 50% to 75% by weight and water in a range 10% to 30%, kneading said mixture in a high speed, high shear mixer to form a substantially homogeneous deformable mass, forming said mass by extrusion under vacuum into a waterproofing sheet, and laminating said sheet with a flexible, porous, carrier sheet to form a laminate structure free of loose particulate material
In this respect, use of a mixer capable of high speeds and high shear action in order to thoroughly mix the liquid and granular components together and knead the resulting mixture is essential to ensure that a homogenous plastic (i.e deformable) mass is obtained .
Subsequent extrusion under vacuum is also essential to ensure removal of any potential air pockets in the mixture and a high density in the final product, which is desirably as thin as practical, so as to be as cost effective as possible.
In order to achieve an even pressure during extrusion, yet obtain a relatively wide, thin sheet of waterproofing material, it has been found particularly advantageous for the plastic mass to be extruded in annular form, using a conical, or bell shaped insert in the extrusion die, for example. Then, immediately after formation, the annulus or pipe can be slit, and supported as appropriate as it in uncurled and brought into contact with the carrier sheet.
After forming the laminate material can be subjected to a drying step to remove excess water from the waterproofing layer and cause it to loose a degree of elasticity so that it is less likely to deform further during transportation and storage. Such drying also increases the swellability of the smectite clay upon contact with water in use.
Union of the smectite containing layer with the carrier sheet can be by adhesive, but desirably no adhesive is used, the mixture of smectite (and other substance(s)) being such as to allow pressure to force the plastic mass into the interstices of the carrier sheet (which is desirably of a textile nature) so as physically to unite the two. Similar connection can be effected between the waterproofing layer and any overlying cover sheet.
Naturally, the invention also provides the waterproofing laminate material, free of loose particulate material, which results from the aforesaid method. Said material comprises a flexible, porous carrier sheet laminated to a waterproofing sheet which is formed by extrusion under vacuum from a substantially homogenous deformable mass consisting of a mixture of particulate smectite clay and a liquid, in which respect the clay is in a range from 50% to 75% by weight of the mixture and the liquid comprises water in a range from 10% to 30% by weight of the mixture.
Additives which modify the behaviour of the smectite clay under certain specified conditions such as salt water, or presence of strong leachates, radiation hydrocarbons or organic chemicals can be added at the mixing stage, particularly to the liquid component of the mixture, to be operative when the smectite is in use.
Organic materials such as methanol, ethanol and other alcohols, glycerine, diesel and other oils and fats can be added to the water.
Alcohols have particular advantages. The y are introduced primarily to increasing the flexibility and reducing the stiffness of the mixture thus assisting in its processing, i.e. a length of the clay can then be bent easily without breaking. Methanol and glycerol are particularly useful additives in this respect. Whilst alcohols are generally expensive, they are also usually far more volatile than water. Thus, a plastic mass made using methyl alcohol can, after having been formed into a cohesive continuous layer be dried using less heat than would be necessary to drive out the water from a similar mass. In addition to this however, the alcohol driven off can be condensed and reused thus offsetting the cost thereof.
The montmorillonite mesh size can be anything from 50 mesh or smaller, desirably, however the size is a maximum of 100. In practice a mesh size of 200 has been found useful although variations downwards from about 100 mesh do work although with less desirable qualities. Finer meshes are perfectly acceptable, but tend to be unnecessary. The smectite used is desirably sodium montmorillonite although calcium montmorillonite (modified by treatment with sodium hydroxide) can be used. As the montmorillonite is usually broken down significantly during mixing to micro sizes, initial grain size is not critical.
The waterproofing sheet may be sandwiched between the carrier sheet and cover sheet.
The fabrics used as carrier sheet and/or cover sheet can be conventional woven or non-woven textile such as nylon or polypropylene or polyester.
Waterproofing material in accordance with the invention can be used, for example, as roofing material or to provide a seal for a pipe or other plumbing fittings.
Acrylate or polyacrylate compounds may desirably be added to the liquid for mixing with the clay. In the sodium cation form the acrylate can replace the sodium cations which normally coat the outer layers of the smectite clay plates. These sodium ions are not readily displaced by calcium or other ions which may be present in leachate or fertilisers contaminated ground water, so that a highly effective barrier, which is resistant to breakdown is formed in this way.
Another advantage of incorporating acrylate or polyacrylate compounds is that adhesive compatible thereto, such as cyano acrylate adhesive, is effective to adhere the resulting sheet material to upright surfaces, such adhesion previously being rather difficult to accomplish due to the ineffectiveness of most adhesives.
A further problem of smectite clay when used as a waterproofing material, is that its function is very dependent on the amount of montmorillonite used. For example when a body of a montmorillonite is constrained between two surfaces, such as the concrete of a structure and the ground, when contacted by water it swells and forms a high pressure layer which prevents ingress of water to the structure and therefore effectively waterproofs it. To increase the waterproofing efficiency of the clay body, larger quantities of montmorillonite can be used. However, higher quantities of montmorillonite mean thicker sheets of material which are more difficult to handle and which are heavier gave more transportation costs and are bulky. In sheets which consist principally of particulate montmorillonite there can be significant difficulty in getting a large quantity into a small area. Sheet material used for waterproofing in ground situation or for roofs, walls and the like tend to have relatively low densities. This is because they are generally made from particulate montmorillonite adhered to a support sheet as of plastics material or textile material and secured thereto by a variety of means ranging from adhesive to needling to sewing or be embedment in a mesh of fibres.
The invention provides a smectite clay waterproofing material having a density greater than 1000 kg mxe2x88x923 (62.43 lb/ft3).
The waterproofing material can be a sheet at least a meter (39.4 inches) wide and desirably up to four meters (157.5 inches) wide or more.
The pressure applied during extrusion, and after a suction treatment which has removed excess air and possible other gases, reduces the number of voids in the product as-well as urging the molecules of the product closer together to produce a denser product.
Reinforcement can be provided in the middle of the smectite containing layer.
The reinforcement can be secured to the cover sheet and/or the support sheet.